JEE Main 2021 · Chemistry · Qualitative and Practical Chemistry · easy

In a Kjeldahl estimation, 1.0 g of an organic compound is digested and the ammonia evolved is absorbed in 50 mL of 0.50 M H2SO4. The unreacted acid…

Numerical answer

In a Kjeldahl estimation,

1.0\ \mathrm{g}

of an organic compound is digested and the ammonia evolved is absorbed in

50\ \mathrm{mL}

0.50\ \mathrm{M}

\mathrm{H_2SO_4}

. The unreacted acid requires

30\ \mathrm{mL}

1.0\ \mathrm{M}

NaOH for complete neutralisation. The percentage of nitrogen in the compound is (N = 14)

Show answer and solution

Answer: 28

Acid taken:

50\ \mathrm{mL}

0.50\ \mathrm{M}

\mathrm{H_2SO_4}

1.0\ \mathrm{N}

, so it is

50

meq. Unreacted acid equals NaOH used:

30\times1.0=30

meq. Acid neutralised by

\mathrm{NH_3}

=50-30=20

meq, which equals

20

mmol of

\mathrm{NH_3}

and hence

20

mmol of N. Mass of N

=20\times10^{-3}\times14=0.28\ \mathrm{g}

. Percentage

=\dfrac{0.28}{1.0}\times100=28

. Treating

\mathrm{H_2SO_4}

as monobasic is the usual error and gives a different answer.

Original question written in the JEE Main 2021 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake